1. Field of the Invention
The present invention relates to a zoom lens system and an imaging apparatus having the zoom lens system and is preferably applied to, for example, a video camera, a silver-halide film camera, and a digital still camera.
2. Description of the Related Art
On photographing an object from a mobile object such as a traveling automobile or airplane, since vibrations are propagated to a photographing system it causes that a photographed image blurs. Various types of shake correction optical systems having a shake correction function for preventing a blur of a photographed image have been proposed so far.
For example, in Japanese Patent Application Laid-Open No. S56-21133, a detection device to detect a vibration state is provided in an optical apparatus, and an image blur is corrected to stabilize an image by moving a portion of optical components of an optical system in the direction for cancelling a vibrational displacement of an image blur due to vibrations in responce to the output signal from the detection device. In Japanese Patent Application Laid-Open No. S61-223819 (corresponding to U.S. Pat. No. 4,927,250), an image blur is corrected by changing apex angles of a variable apex angle prism according to vibrations of a photographing system in which the variable apex angle prism is disposed in a position closest to an object to stabilize an image. In Japanese Patent Application Laid-Open No. H02-124521 (corresponding to U.S. Pat. No. 5,039,211), a static image is obtained by detecting vibrations of a photographing system by a detection device such as an acceleration sensor and displacing a portion of lens units of the photographing system in the direction perpendicular to the optical axis in accordance with a signal thus obtained.
In Japanese Patent Application Laid-Open No. H07-128619, in a four-unit configuration zoom lens composed of first, second, third and fourth lens units of positive, negative, positive and positive refractive powers, a static image is obtained by constituting the third lens unit by two lens sub-units of positive and negative refractive powers and displacing the lens sub-unit having positive refractive power of the two lens sub-units in the direction perpendicular to the optical axis. In Japanese Patent Application Laid-Open No. H07-199124 (corresponding to U.S. Pat. No. 5,585,966), in a four-unit configuration zoom lens composed of first, second, third and fourth lens units of positive, negative, positive and positive refractive powers, a static image is obtained by displacing the whole third lens unit in the direction perpendicular to the optical axis. In Japanese Patent Application Laid-Open No. H05-60974, in a four-unit configuration zoom lens composed of first, second, third and fourth lens units of positive, negative, positive and positive refractive powers, the whole length of lenses is shortened by using the third lens unit as the telephoto type lens constituted by a positive lens and a negative meniscus lens.
Moreover, in Japanese Patent Application Laid-Open No. 2001-66500 (corresponding to U.S. Pat. No. 6,414,800), in a four-unit configuration zoom lens composed of first, second, third and fourth lens units of positive, negative, positive and positive refractive powers, the present applicant proposes a zoom lens for obtaining a static image by displacing the whole third lens unit in the direction perpendicular to the optical axis.
Furthermore, in Japanese Patent Application Laid-Open No. H11-237550 (corresponding to U.S. Pat. No. 6,473,231 and U.S. Pat. No. 6,606,194), in a four-unit configuration zoom lens composed of first, second, third and fourth lens units of positive, negative, positive and positive refractive powers, the present applicant proposes a zoom lens for obtaining a static image by dividing the third lens unit into a lens sub-unit of negative refractive power and a lens sub-unit of positive refractive power and displacing the lens sub-unit of positive refractive power in the direction perpendicular to the optical axis.
Furthermore, in Japanese Patent Application Laid-Open No. H10-260355 (corresponding to U.S. Pat. No. 6,473,231 and U.S. Pat. No. 6,606,194), in a four-unit configuration zoom lens composed of first, second, third and fourth lens units of positive, negative, positive and positive refractive powers, the present applicant proposes a zoom lens for obtaining a static image by dividing the third lens unit into two positive lens sub-units and displacing either of them in the direction perpendicular to the optical axis.
Japanese Patent Application Laid-Open No. H11-344669 (corresponding to EPA1 1103834) discloses a zoom lens for obtaining a static image by displacing the third lens unit or fourth lens unit in the direction perpendicular to the optical axis in a five-unit configuration zoom lens composed of first to fifth lens units of positive, negative, positive, genitive and positive refractive powers or positive, negative, negative, positive and positive refractive powers.
Moreover, Japanese Patent Application Laid-Open No. H10-232420 discloses a zoom lens for obtaining a static image by constituting the third lens unit by two lenses of a positive lens and a negative lens and displacing either of the two lenses in the direction perpendicular to the optical axis in a four-unit configuration zoom lens composed of first, second, third and fourth lens units of positive, negative, positive and positive refractive powers.
Furthermore, Japanese Patent Application Laid-Open No. H09-230235 (corresponding to U.S. Pat. No. 6,266,189 and U.S. Pat. No. 6,285,502) discloses a zoom lens for obtaining a static image by constituting a zoom lens having a four-unit configuration composed of first, second, third and fourth lens units of positive, negative, positive and positive refractive powers so that the first and fourth lens units move toward the object side when zooming from a wide angle end to a telescopic end displacing one of the lenses behind the second lens unit in the direction perpendicular to the optical axis.
Furthermore, Japanese Patent Application Laid-Open No. H09-230241 (corresponding to U.S. Pat. No. 6,266,189 and U.S. Pat. No. 6,285,502) discloses a zoom lens for obtaining a static image by constituting a zoom lens having a four-unit configuration formed by first, second, third and fourth lens units of positive, negative, positive and positive refractive powers so that the first and fourth lens units move toward the object side when zooming from a wide angle end to a telescopic end, dividing any one of the lens units from the second lens unit downward into two lens sub-units and displacing either of the two lens sub-units in the direction perpendicular to the optical axis.
In general, when disposing a shake correction optical member (such as a variable apex-angle prism or movable lens unit) to the front of a photographing system, there has been a problem that the whole apparatus is increased in size and a moving mechanism for moving its variable apex-angle prism or movable lens unit becomes complex.
For example, in an optical system for having a variable apex-angle prism, for shake correction there has been a problem that the occurrence of eccentric chromatic aberration of magnification increases particularly at the long-focal-length side when performing the shake correction.
However, a method for preventing vibrations by decentering some lenses of a photographing system in the direction perpendicular to the optical axis in parallel has an advantage that a special optical system is unnecessary for shake correction. Moreover, by minimizing the configuration of lens units for shake correction, it is an advantage that it is possible to restrain the driving torque and downsize an actuator for shake correction.
From the above viewpoint, in the case of a zoom lens having a four-unit configuration composed of first, second, third and fourth lens units of positive, negative, positive and positive refractive powers among the above well-known zoom lenses, if the vibration proof is performed by moving some lenses of the third lens unit instead of the whole third lens unit in the direction perpendicular to the optical axis, the driving torque can be decreased. Particularly, it is effective to prevent vibrations by one thin lens component.
However, in Japanese Patent Application Laid-Open No. H10-260355, vibrations are prevented by driving two lenses including a lens having a comparatively large wall thickness as a shake correction lens unit. In the case of this method, the driving torque tends to increase.
In a four-unit configuration zoom lens composed of first, second, third and fourth lens units having positive, negative, positive and positive refractive powers respectively, when dividing the third lens unit into a lens sub-unit of negative refractive power and a lens sub-unit of positive refractive power, the back focus is likely to be lengthened due to the function of the lens sub-unit of negative refractive power. This is effective when inserting a color separating prism but is disadvantageous to decrease the whole lens length.
In the methods proposed in Japanese Patent Application Laid-Open Nos. H11-237550 and H10-232420, the third lens unit is divided into a lens unit of negative refractive power and a lens unit of positive refractive power and the whole lens length tends to increase due to the function of the lens unit of negative refractive power.
In Japanese Patent Application Laid-Open No. 11-344669, the third lens unit or the fourth lens unit in a five-unit configuration is a lens unit of negative refractive power. However, this is equivalent to a configuration in which the third lens unit in a four-unit configuration is divided into two lens units and either of them has negative refractive power. Therefore, the whole length tends to increase due to the function of the lens unit of negative refractive power.
In a four-unit configuration zoom lens composed of first, second, third and fourth lens units having positive, negative, positive and positive refractive powers respectively, in order to focus by the fourth lens unit it is necessary to sufficiently secure the interval between the third lens unit and fourth lens unit in the telescopic side having a large delivery distance of a lens unit. In the case of a high zooming ratio such as approx. 10, with the fourth lens unit having reciprocated locus being convex to the object side, a preferable space efficiency is obtained by securing a delivery space when focusing on infinite objects at the telescopic side in comparison with the case focusing on close-range objects. Therefore, it is easy to cope with both to obtain a high zooming ratio and to downsize the zoom lens.
However, in Japanese Patent Application Laid-Open Nos. H09-230241 and H09-230235, the fourth lens unit moves toward the object side from the wide angle end toward the telescopic end to decrease the interval with the third lens unit. Therefore, to secure the interval for the fourth lens unit to be delivered at the telescopic end, the whole length increases. Therefore, in the case of this method, it is difficult to cope with both rear focusing and decrease of the whole lens length.